I'm building a wheel with double butted spokes, 2.0 mm at the ends, 1.8 mm in the center. The Park Tool Spoke Tension Meter has a conversion sheet to determine the tension in spokes of different diameters. My question is which scale to use: 2.0 mm or 1.8 mm.
Logically, I think that I should use the 1.8 conversion, because the center of the spoke is 1.8 mm diameter. But the entire length of the measured section is probably not 1.8 mm, because it is tapering to 2.0 mm at the ends.
The answer to this question suggests there is some acceptable variation, so I was thinking about aiming for somewhere in between.